On Wed, Jul 08, 2015 at 10:59:44AM +0100, Peter Zijlstra wrote:

On Tue, Jul 07, 2015 at 03:28:13PM -0400, Waiman Long wrote:

quoted

#ifndef queued_inc_reader_return
static inline u32 queued_inc_reader_return(struct qrwlock *lock)

That's actually a misleading name, we don't do an inc_return, we do a
fetch_inc.

quoted

{
    return atomic_add_return(_QR_BIAS, &lock->cnts) - _QR_BIAS;
}
#endif

With that you (Will) could even reuse the ll/sc load and avoid issuing a
second load. You basically need atomic_fetch_add_relaxed().

ARMv8.1 has an instruction for that :) [ldadd].

Will